In my travels, when I broach the subject of making webpages easier to use, the number one concern most have is that if they change their websites, it may alienate some of their older members who finally got used to a certain way of online banking. To this I say:
They'll get over it.
Riddle me this: When you decide to remodel your lobby, do you worry that people will not be able to find the teller counter?
There is no reason, in 2010, to continue to have a cluttered, unattractive website simply to appease older members. Much like your lobby, if you put enough thought and research into make your interface clean and easy to use, it shouldn't matter how much you change it, because it should just work.
As I've said many times before on the show, a stagnant, stale website may appease some of your members, but will alienate most of your potential new credit union customers. Though it may take a while for them to get acclimated, once they understand how your new site works, its water under the bridge.
I remember being realllly upset about Facebook's first major website overhaul - most of my friends were as well. But today, years later, I couldn't even tell you what the old interface looked like.
That isn't to say you should change something every day - work hard to get it right and its not something you'll have to do often.
I've said it once, I've said it twice, and I'll say it until I die: Your website is one of the most important parts of your identity as a company. Invest in it and you can't go wrong.